1. Technical Field
The present invention relates to an evaluation method of residual stress in water jet peening and a method of executing a water jet peening, and more particularly to a evaluation method of residual stress in water jet peening and a method of executing water jet peening suitable for applying to water jet peening executed in a boiling water reactor.
2. Background Art
In boiling water nuclear plants and pressurized water nuclear plants, stress corrosion cracks in a reactor internal, which is a structure member, are suppressed by executing, for example, water jet peening to convert tensile residual stress generated in the reactor internal during welding or machining to compressive residual stress. Water jet peening (hereinafter, referred to as WJP) is a technology to convert tensile residual stress generated in a surface of the reactor internal to compressive residual stress by applying WJP to the surface. In this WJP, water under high pressure is jetted from a nozzle in water to the surface of the reactor internal in a state in which the surface on which the WJP is executed is in contact with the water. When fine bubbles (cavitation bubbles) included in the jetted high-pressure water are collapsed, impulse waves are generated. The generated impulse waves impinge on the surface and the tensile residual stress generated in the surface is then converted to compressive residual stress (see “Noboru Saito et al., Development of Water Jet Peening Technology for Nuclear Plants and Incore Devices, Jet Flow Engineering, Vol. 20, No. 1 (2003), pp. 4-12, Water Jet Technology Society of Japan”).
Some technologies to evaluate residual stress generated in a structure member on which WJP was executed (compressive residual stress, for example) are also proposed.
Japanese Patent Laid-open No. 2009-209792 describes a method of predicting erosion generated by cavitation on an internal flow path of a hydraulic machine. In this method, a piezoelectric device is provided on an inner surface of an internal flow path of an actual hydraulic machine (or a hydraulic machine model), and a light emitting device, which converts a voltage signal generated by the piezoelectric device to light, is provided at a predetermined position on the hydraulic machine. When cavitation is generated, the light emitting device emits light. The generated light is measured to predict an area of the internal flow path over which erosion occurs and to predict the amount of erosion.
Japanese Patent Laid-open No. 2008-155345 describes a method of evaluating residual stress on a surface to which water jet peening was executed. In this residual stress evaluation method, a whole area of water jet peening traces generated per unit area on a surface on which WJP was executed is measured, the whole peening trace area is substituted into a relational expression between the residual stress and the whole peening trace area, and the residual stress on the surface on which WJP was executed is evaluated according to the obtained calculation result.
In “Noboru Saito et al., Development of Water Jet Peening Technology for Nuclear Plants and Internal Equipments, Jet Flow Engineering, Vol. 20, No. 1 (2003), pp. 4-12, Water Jet Technology Society of Japan”, residual stress is measured by an X-ray diffraction method to evaluate an effect of WJP executed on a structure member.
In “Masashi Fukaya et al., Development of Water Jet Peening (WJP) (3), Flow Behavior Evaluation in WJP, Japan Society of Mechanical Engineers No. 09-3, M&M 2009 Conference 0S1431, Jul. 24 to 26, 2009, pp. 333-334”, the internal pressure pB of a cavitation bubble is calculated from equations (1) to (4) (see page 333) through jet flow analysis, and the calculated bubble's internal pressure pB is substituted into equation (5) (see page 333) to calculate cavitation strength I. In the paper written by Masashi Fukaya et al., the cavitation strength I is also used to predict compressive residual stress generated in a SUS plate after WJP execution.
In “Hisamitsu Hatou et al., Development of Water Jet Peening (WJP) (4), Residual Stress Improvement Behavior Evaluation in WJP), Japan Society of Mechanical Engineers No. 09-3, M&M 2009 Material & Mechanics Conference 2009, CD-ROM Transactions, 0S1431, Jul. 24 to 26, 2009, pp. 335-336” as well, a method of evaluating residual stress in the depth direction after WJP execution is described. In this evaluation method, residual stress in a depth direction after WJP execution is evaluated according to collapse pressure of cavitation.